Pulse oximetry to detect paediatric hypoxaemia—the fifth vital sign
Authors: Heather J Zar, Eric D McCollum
Journal: The Lancet Global Health (2023)

Pneumonia or lower respiratory infection remains a major cause of morbidity and mortality in children younger than 5 years, with most of the approximately 672 000 childhood pneumonia deaths in 2019 occurring in low-income and middle-income countries (LMICs).1Global Burden of Disease Collaborative NetworkGlobal Burden of Disease study 2019 (GBD 2019) results.https://vizhub.healthdata.org/gbd-results/Date: 2020Date accessed: July 20, 2023Google Scholar Almost all childhood pneumonia deaths are preventable or treatable; important mortality risk factors include hypoxaemia (low peripheral arterial oxyhaemoglobin saturation [SpO2] measurement by pulse oximetry), malnutrition, anaemia, or underlying chronic conditions. Childhood pneumonia death is driven by inadequate recognition of illness severity, mortality risk, and lack of appropriate, timely treatment, including medical oxygen. In LMICs, four vital signs are used to assess childhood illness severity: heart rate, respiratory rate, blood pressure, and temperature. Of these, only respiratory rate is utilised for pneumonia management per WHO Integrated Management of Childhood Illness (IMCI) guidelines, the backbone of childhood pneumonia management for three decades in LMICs. WHO IMCI guidelines recommend antibiotics and hospital referral for severe pneumonia or home-based care with oral antibiotics for non-severe pneumonia.2WHOIntegrated management of childhood illness: chart booklet.https://apps.who.int/iris/bitstream/handle/10665/104772/9789241506823_Chartbook_eng.pdfDate: March, 2014Date accessed: July 20, 2023Google Scholar In the absence of oximetry, such categorisation rests predominantly on clinical acumen. Hypoxaemia is common in children with pneumonia. In a large 2023 analysis of in-hospital childhood pneumonia mortality, almost 20% of children with pneumonia characterised by chest indrawing were hypoxaemic, of whom 10% died.3Hooli S King C McCollum ED et al.In-hospital mortality risk stratification in children aged under 5 years with pneumonia with or without pulse oximetry: a secondary analysis of the Pneumonia REsearch Partnership to Assess WHO REcommendations (PREPARE) dataset.Int J Infect Dis. 2023; 129: 240-250Summary Full Text Full Text PDF PubMed Google Scholar A 2022 meta-analysis of children hospitalised with pneumonia in LMICs reported hypoxaemia in 31% of all WHO-defined pneumonia cases and in 41% of severe cases.4Rahman AE Hossain AT Nair H et al.Prevalence of hypoxaemia in children with pneumonia in low-income and middle-income countries: a systematic review and meta-analysis.Lancet Glob Health. 2022; 10: e348-e359Summary Full Text Full Text PDF PubMed Scopus (22) Google Scholar To date, hypoxaemia measurement using pulse oximetry has not been prioritised in IMCI guidelines for primary care, which is where most children initially present. As IMCI guidelines frequently miss hypoxaemia when pulse oximeters are unavailable and clinical signs are used alone, many children who require oxygen are not referred, contributing to pneumonia-associated mortality. A 2023 study in Bangladesh of approximately 4000 children aged 3–11 months with suspected ambulatory pneumonia showed that WHO IMCI guidelines that did not have oximetry missed approximately 88% of children with an SpO2 less than 90% who should have been referred, and all subsequent deaths in children with an SpO2 less than 90%.5McCollum ED Ahmed S Roy AD et al.Risk and accuracy of outpatient-identified hypoxaemia for death among suspected child pneumonia cases in rural Bangladesh: a multi-facility cohort study.Lancet Respir Med. 2023; 11: 769-781Summary Full Text Full Text PDF PubMed Scopus (4) Google Scholar Similarly, a Malawian study of more than 13 000 children in rural health centres found that approximately 69% of children with an SpO2 less than 90% would not have been referred without oximetry.6McCollum ED King C Deula R et al.Pulse oximetry for children with pneumonia treated as outpatients in rural Malawi.Bull World Health Organ. 2016; 94: 893-902Crossref PubMed Scopus (55) Google Scholar In hospitals, guidelines indicate that pulse oximetry should be done where feasible and oxygen initiated when SpO2 is less than 90%. However, a secondary analysis from more than 164 000 children hospitalised with pneumonia found that the absence of oximetry was associated with more than double the case fatality compared with when oximetry was completed.3Hooli S King C McCollum ED et al.In-hospital mortality risk stratification in children aged under 5 years with pneumonia with or without pulse oximetry: a secondary analysis of the Pneumonia REsearch Partnership to Assess WHO REcommendations (PREPARE) dataset.Int J Infect Dis. 2023; 129: 240-250Summary Full Text Full Text PDF PubMed Google Scholar Hypoxaemia has been consistently and strongly associated with childhood pneumonia mortality risk. Although WHO defines hypoxaemia as an SpO2 of less than 90%, increasing evidence indicates that even moderate hypoxaemia with an SpO2 of 90–93% conveys a substantially elevated risk of death. A meta-analysis reported that SpO2 less than 90% was associated with a 5·5-fold increased mortality risk, but that an SpO2 of 90–93% also increased such risk.7Wilkes C Bava M Graham HR Duke T What are the risk factors for death among children with pneumonia in low- and middle-income countries? A systematic review.J Glob Health. 2023; 1305003Crossref PubMed Scopus (2) Google Scholar Notably, when using an SpO2 of less than 90% for referral, approximately 40% of children in Bangladesh who subsequently died of pneumonia were identified by IMCI guidelines, but an SpO2 of less than 94% (or a failed measurement) identified approximately 63% of subsequent deaths and had the greatest sensitivity for mortality risk.5McCollum ED Ahmed S Roy AD et al.Risk and accuracy of outpatient-identified hypoxaemia for death among suspected child pneumonia cases in rural Bangladesh: a multi-facility cohort study.Lancet Respir Med. 2023; 11: 769-781Summary Full Text Full Text PDF PubMed Scopus (4) Google Scholar Although children in Bangladesh with an SpO2 less than 90% had a 10-fold higher mortality risk than those with an SpO2 more than 94%, those with an SpO2 of 90–93% had a more than 4-fold risk of mortality. These data indicate that SpO2 thresholds for defining hypoxaemia and identifying children at high mortality risk should be reconsidered to SpO2 less than 94%, dependent on geographical location (including altitude) and health system capacity. Availability of suitable oximeters, especially for children younger than 5 years, health-care worker training, and inadequate referral pathways or oxygen remain obstacles to more widespread oximetry and oxygen use. Although there has been a lack of high-quality, durable, low-cost oximeters suitable for children in LMICs, technological advances have led to manufacture of more child-appropriate devices. Research in Bangladesh demonstrated that primary health-care workers could effectively use pulse oximetry in children following abbreviated training, with 99% of assessments successful and measurement completion at a median of 36 s.8Rahman AE Ameen S Hossain AT et al.Introducing pulse oximetry for outpatient management of childhood pneumonia: an implementation research adopting a district implementation model in selected rural facilities in Bangladesh.EClinicalMedicine. 2022; 50101511Summary Full Text Full Text PDF Scopus (4) Google Scholar The COVID-19 pandemic also showed that upscaling of oximetry and oxygen therapy is achievable in LMICs, although adults were prioritised. Higher costs of quality paediatric devices and measurement accuracy issues remain ongoing challenges.9Sjoding MW Dickson RP Iwashyna TJ Gay SE Valley TS Racial bias in pulse oximetry measurement.N Engl J Med. 2020; 383: 2477-2478Crossref PubMed Scopus (369) Google Scholar In summary, SpO2 measured by pulse oximetry is an essential fifth vital sign in all sick children. This feasible non-invasive procedure can effectively identify children at high mortality risk for referral and oxygen therapy. Although work remains to optimise oximetry for children in LMICs, revision of global guidelines to include oximetry at all care levels should be a priority. Oximetry with referral or oxygen therapy to manage hypoxaemic pneumonia and reduce childhood mortality should be core to health systems in LMICs—such standards are routine in high-income countries. Oximetry and appropriate oxygen therapy for sick children are fundamental to reduce health inequity and strengthen child health globally. HJZ reports grants for studies in childhood pneumonia from the Bill & Melinda Gates Foundation (OPP1017641, OPP1017579), National Institutes of Health (U54HG009824, UO1AI1104660), Medical Reseach Council, and the Wellcome Trust. EDM holds grants for studies in childhood lower respiratory infection from the Bill & Melinda Gates Foundation, National Institutes of Health, United States Agency for International Development, Centers for Disease Control, and Thrasher Research Fund.